EP2513459A1

EP2513459A1 - Diagnostic method for a diesel engine

Info

Publication number: EP2513459A1
Application number: EP10798531A
Authority: EP
Inventors: David Deregnaucourt; Charles Platteau
Original assignee: Spheretech International SA
Current assignee: Ecosphere SA
Priority date: 2009-12-14
Filing date: 2010-12-14
Publication date: 2012-10-24
Also published as: LU91630B1; WO2011073175A1

Abstract

The present invention is related to a diagnostic method for a Diesel engine for determining whether said engine is affected by one or several malfunctions negatively impacting the degree of pollution of the exhaust gases produced by said engine, comprising the steps of providing a Diesel engine comprising a motor block, air intake means, exhaust gas outlet means and fuel injection means, measuring, according to a predetermined state of said engine, the level, or the evolution of said level, of a first exhaust gas emitted by the internal combustion engine, said exhaust gas being selected from the group consisting in carbon dioxide (CO₂), carbon monoxide (CO), nitrogen oxides (NO_x) and unburnt hydrocarbons (HC) or a combination thereof, measuring the overall exhaust gas output, measuring at least one operating parameter, said operating parameter being selected from the group consisting of engine speed, engine charge, air inflow, forced induction pressure, water temperature, pressure of the high pressure feeding circuit, fuel inflow, set point of opening of the exhaust gas recirculation valve, individual injector volume correction, exhaust gas temperature, differential pressure on the particulate filter or a combination thereof, and analysing the measures performed by a comparison of said measures to the ones being characteristic of one or several predetermined normal or abnormal states of said engine, deducing from said measures, a malfunction affecting said engine.

Description

DIAGNOSTIC METHOD FOR Ά DIESEL ENGINE

Field of the Invention

[0001] The present invention relates to a diagnostic method for an internal combustion engine through the measure of the level, or evolution of the level of at least one exhaust gas, at least one operating parameter and the overall exhaust gas output, and relates also to a device for implementing said method.

State of the Art

[0002] Fight against pollution, regardless of its origin, has been at the core of international discussions for years. All motorized vehicles, including the automobile, have been recognized as being at least partially responsible for the ever-increasing emission of polluting gases in the environment. Therefore, manufacturers have been urged to find technical solutions to efficiently reduce the level of polluting emissions generated by these motorized vehicles .

[0003] Considerable progress has been made by car manufacturers to control and/or limit emission of polluting exhaust gases generated by motorized vehicles by introduction of effective pollution control systems, such as for example particulate filters or EGR (Exhaust Gas Recirculation) systems.

[0004] Generally, the conception of a motorized vehicle takes into account the current environmental requirements, new vehicles could therefore be considered as clean vehicles. However, these vehicles have to remain clean during their entire lifetime while facing malfunctions, in particular engine malfunctions, which could impact the level of pollution of the vehicles. [ 0005 ] Among engine malfunctions, EGR valve malfunctions are important issues as a Diesel engine works in surplus air mode and produces thus strong emissions of nitrogen oxides (NOx) . Indeed the EGR valve re-injects the exhaust gases into the intake, thereby delaying the flash point, and thereby reducing the formation of NO_x. A dysfunction leads thus to an increase of pollution.

[ 0006 ] The combustion of a Diesel engine, as perfect as it may be, creates also soot in addition to particles. This soot causes a sooting up of the EGR valve and the intake manifold at variable mileages. Any geometric modification of the intake manifold (narrowing of the conduits due to sooting) will cause a malfunction for lack of air filling. The performance and power of the engine will be greatly affected.

[ 0007 ] The exhaust line and the pollution control system can also clog, intensifying the engine malfunctions. When the pollution control system becomes inoperative, the computer controls the EGR valve in the closed position, but also reduces the engine performance by limiting the supercharging pressure.

[ 0008 ] Devices and methods for engine control are known. For example, US 2002/157458 describe a method to measure carbon dioxide in the re-circulated air of an engine's pre- combustion. US6457461 disclose a system and a method for diagnosing a component failure in an internal combustion engine to divert exhaust gas from the engine exhaust to the engine intake. US 2003/191575 describe a system and a method for estimating nitrogen oxides (NO_x) content of exhaust gas produced by an internal combustion engine to determine the correct proportions of air, fuel and exhaust gas to control the engine, EGR system and/or turbocharger . Whereas, DE 10 2005013936 discloses measurements of carbon dioxide levels to monitor the normal or sufficient regeneration of a Diesel engine particle filter in an exhaust line. [0009] On the other hand, a number of methods exist to determine whether engine's exhaust gases exceed the prescribed admissible atmospheric pollution values, such as, for example, the one described in BE 844622 which proposes, in particular, analyzing the engine's exhaust gases in order to determine whether, for different prescribed control modes, their levels exceed the stipulated admissible atmospheric pollution values in carbon monoxide (CO) and hydrocarbon (HC) .

[0010] However, there is a need for a method and a device suitable to diagnose the malfunction affecting the vehicles and the vehicles engine so as to repair them to keep a low level of pollution.

Aims of the invention

[0011] The present invention aims to provide a method and a device which does not have the drawbacks of the prior art .

[0012] The invention aims to provide an improved method and device to diagnose a malfunction of the engine of a vehicle which may impact the level of pollution of exhaust gases produced by said engine.

[0013] The invention aims to provide a method and device to diagnose if a Diesel engine is affected by a malfunction which alters the engine's performance, which may cause a breakdown of the engine, or to determine whether the engine is defective.

Summary of the Invention

[0014] The present invention is related to a diagnostic method for a Diesel engine for determining whether said engine is affected by one or several malfunctions negatively impacting the degree of pollution of the exhaust gases produced by said engine, comprising the steps of:

a) providing a Diesel engine comprising a motor block, air intake means, exhaust gas outlet means and fuel injection means .

b) measuring, according to a predetermined state of said engine, the level, or the evolution of said level, of a first exhaust gas emitted by the internal combustion engine, said exhaust gas being selected from the group consisting in carbon dioxide (C0₂), carbon monoxide (CO), nitrogen oxides (NO_x) and unburnt hydrocarbons (HC) or a combination thereof,

c) measuring the overall exhaust gas output,

d) measuring at least one operating parameter, said operating parameter being selected from the group consisting of engine speed, engine charge, air inflow, forced induction pressure, water temperature, pressure of the high pressure feeding circuit, fuel inflow, set point of opening of the exhaust gas recirculation valve, individual injector volume correction, exhaust gas temperature, differential pressure on the particulate filter or a combination thereof, and

e) analysing the measures performed at steps b) and d) or at steps b), c) and d) by a comparison of said measures with the ones being characteristic of one or several predetermined normal or abnormal states of said engine, f) deducing from the analysis of said measures, a malfunction affecting said engine.

[0015] According to particular embodiments, the method may comprise one, or a combination, of any of the following characteristics:

- the steps b) and d) or b), c) and d) are performed simultaneously, - the level or evolution of the level of the first exhaust gas is measured in combination with the level, or evolution of the level, of at least another exhaust gas, said another exhaust gas being oxygen when the first exhaust gas is carbon dioxide, or said another exhaust gas being unburnt hydrocarbons or nitrogen oxides when the first exhaust gas is carbon monoxide,

according to a predetermined operating state of the engine, the level of the first exhaust gas, alone or in combination with at least another exhaust gas, is measured and compared to a first level of said exhaust gas measured for a state representing a normal operation of said engine and/or compared to a second level of said exhaust gas measured for a state representing a abnormal operation of said engine and characterizing a predetermined malfunction, and from said comparison, deducing that said engine is affected by said predetermined malfunction,

- the step c) is performed by measuring of differential pressure,

- the step c) is performed with a Pitot tube,

- the method further comprises the steps of calculating, from the measuring of steps b) and c), the emission value (in g/h or g/km) of the at least one exhaust gas emitted by the internal combustion engine, and comparing the calculated emission value of the at least one exhaust gas emitted by the internal combustion engine with a predetermined emission limit of the at least one exhaust gas.

[0016] Another aspect of the present invention is related to a device to diagnose a Diesel engine malfunction negatively impacting the degree of pollution of the exhaust gases produced by said engine, said device comprising means for measuring at least a first exhaust gas selected from the group consisting in carbon dioxide (C0₂), carbon monoxide (CO), and unburnt hydrocarbons (HC) and nitrogen oxides ( ΝΟχ ) , or a combination thereof, means for measuring the total output of the overall exhaust gas, and means for measuring at least one operating parameter selected from the group consisting of engine speed, engine charge, air inflow, forced induction pressure, water temperature, pressure of the high pressure feeding circuit, fuel inflow, set point of opening of the exhaust gas recirculation valve, individual injector volume correction, exhaust gas temperature and differential pressure on the particulate filter, means for analysing the level, or evolution of the level of said exhaust gas and said overall exhaust gas output, and analysing said operating parameters, or the evolution of said operating parameters, performing a comparison with the ones being characteristic of one or several predetermined normal or abnormal states of said engine, processing means enable to characterize a malfunction affecting said engine.

[0017] According to particular embodiments, the device may comprise one, or a combination, of any of the following characteristics:

- the means for measuring at least a first exhaust gas comprise at least one gas analyzer comprising at least one measuring cell,

- the device comprises means for calculating the emission value of the at least one exhaust gas with a pre-determined emission limit of said at least one exhaust gas,

- the means for measuring the total output of the overall exhaust gas operate by measuring of differential pressure,

- the means for measuring the total output of the overall exhaust gas comprise a Pitot tube,

[0018] The present invention further disclose a computer program executable on the device according to the invention containing instructions that, when executed, perform the method steps of the method according to the invention .

Short description of the drawings

[0019] Figure 1 represents schematically a Diesel engine .

Detailed Description of the Invention

[0020] The diagnostic method and the diagnostic device according to the present invention diagnose one or several malfunctions of an internal combustion engine, more particularly malfunctions of a Diesel engine.

[0021] As all common heat engines, a Diesel engine, illustrated as an example in figure 1, comprises a motor block 1, or motor unit, air intake means, exhaust gas outlet means and fuel injection means.

[0022] The air intake means comprise a supercharging air supply circuit 2, atmospheric air inlet 5, a turbocharger 4.

[0023] The exhaust gas outlet means comprise an exhaust gas conduit 3, an exhaust gas recirculation (EGR) valve 7 and a an exhaust line.

[0024] Also provided a bleed line for bleeding of exhaust gas on the exhaust gas conduit 3 and an EGR valve 7 controlling the admission of these exhaust gases bled through the line 6 in the intake circuit, i.e. here the supercharging air supply circuit 2.

[0025] The exhaust gas in the exhaust gas conduit 3 drive the turbocharger 4 and can be processed through a catalyst and a particle filter, not shown in the figure, then discharged into the environment through the exhaust line .

[0026] The fuel injection means comprise direct injection means or indirect injection means. These means further comprise injectors 8, a common rail 9 supplying the injectors 8 in diesel oil and a high-pressure injection pump 10 or a distributor-type fuel injection pump.

[0027] Therefore, in a preferred embodiment, the Diesel engine comprises an exhaust gas recirculation valve, a common rail injector system, a flow regulator of the common rail injection system, a high pressure pump, a distributor- type pump of the fuel injection system, a injection circuit, injectors, a turbocharger comprising bearings, an intake circuit, an exhaust line, and an air filling system.

[0028] In another embodiment, the Diesel engine do not comprise a turbocharger and the common rail 9 and the high- pressure injection pump 10 are replaced by a distributor- type fuel injection pump.

[0029] The Diesel engine may further comprise engine control unit 11 (ECU) to acquire engine or vehicle operating parameters and/or to control engine elements, for example to control an EGR valve 7 or the high-pressure injection pump 10, to keep the engine running.

[0030] The engine control unit 11 is connected to a plurality of sensors to measure input parameters, such as for example, but not limited to, the engine temperature, position of the accelerator pedal, fuel pressure in the fuel high pressure circuit or common rail circuit. The ECU 11 acquire the parameters in real-time and calculate output parameters such as opening and closing the injectors 8, modifying target pressure in the high pressure circuit, opening or closing the EGR valve 7. It also calculates individual injector parameters through injector flow correction parameters, adapting the injection duration to real injected fuel volume.

[0031] Optionally, the engine control unit 11 also controls individual injectors volume control, for fine tuning the real amount of fuel injected in each cylinders on each cycles .

[0032] The diagnostic device 20, according to the present invention, comprises means for measuring the level or the evolution of the level of at least a first exhaust gas selected from the group consisting in carbon dioxide (C0₂), carbon monoxide (CO), and unburnt hydrocarbons (HC) and nitrogen oxides (NO_x) or for measuring a combination thereof .

[ 0033 ] In a preferred embodiment, the diagnostic device 20 comprises a multi-gas analyzer 21 comprising several gas detectors present in the form of an optical bench comprising at least one measuring cell detecting hydrocarbons (HC), carbon monoxide (CO) carbon dioxide (C0₂), and oxygen (0₂) and nitrogen oxide (NO_x) detection cells, for example of the type marketed by the company City Technology, able to measure gas levels.

[ 0034 ] The exhaust gases measured by the measuring cells are carbon dioxide (C0₂), carbon monoxide (CO), oxygen (0₂), nitrogen oxide (NOx) unburnt hydrocarbons (such as hexane and propane, for example) or a combination thereof.

[ 0035 ] The measure of the level or evolution of the level of the exhaust gases is performed by a collection tube 22 of the gas analyzer 21 introduced into the exhaust line; however, in another embodiment the analysis may be done at the outlet of the exhaust line. It is also possible to implement a system comprising detectors coupled to means for analyzing signals emitted by gas detectors, in order to calculate the respective gas levels.

[ 0036 ] The diagnostic device 20 comprises means for measuring the level, or evolution of the level, of the overall exhaust gas output. These means preferably comprise means for measuring a differential pressure. Preferably the means comprise a pressure sensor/transmitter, such as, for example, the one commercialized by the Kimo^® company. Other suitable means for measuring the pressure include pressure transducers, such as those commercialized by the Farnell^® company. More preferably the means comprise a Pitot tube, such as, for example, the one commercialized by Kimo^® company . [0037] The diagnostic device 20 comprises means for measuring at least one operating parameter of the Diesel engine. These means may be independent of the engine. In a preferred embodiment, the means are connected to the ECU 11 of the engine through the interface 30 by a connection 31.

[0038] The means for determining at least one operating parameter determine preferably the engine speed (rpm), engine charge (% or V), i.e. the accelerator pedal position, air inflow (mg/ stroke ) , forced induction pressure (bars), water temperature (°C), pressure of the high pressure feeding circuit (bars), fuel inflow (mm³/stroke ) , set point of opening of the exhaust gas recirculation valve

(%), individual injector volume correction (mm³/stroke ) , exhaust gas temperature (°C) and differential pressure on the particulate filter (mbars).

[0039] The diagnostic device 20 comprises means for analysing the level, or the evolution of said level, of the exhaust gas, analysing the operating parameters or the evolution of said operating parameters, and analysing the level, or evolution of the level of the overall exhaust gas output, according to one or several predetermined states of said engine.

[0040] The predetermined state of the engine has to be understood as being any suitable engine speed.

[0041] The means for analysing the level, or the evolution of said level, of the exhaust gas and of the overall exhaust gas output, and for analysing the operating parameters, or the evolution of said operating parameters, perform a comparison between the measures obtained during the diagnostic of the engine and the level, or evolution of said level, of the exhaust gas and of the overall exhaust gas output and the operating parameters, or evolution of said operating parameters, known to be characteristic of one or several predetermined normal or abnormal states of the engine. [0042] The diagnostic device 20 further comprises processing means 23 for interpreting the values obtained by the measuring means and interpreting the comparisons performed using the analysing means.

[0043] The processing means 23 may comprise the means for analysing the level, or the evolution of said level, of the exhaust gas, analysing the operating parameters and/or analysing the exhaust gas output .

[0044] The processing means 23 comprise a computer, comprising a central processing unit, random access memory (RAM) and read only memory (ROM), input/output units interconnected by buses, and a power supply.

[0045] The processing means 23 are part of the diagnostic device dedicated to the implementation of the diagnostic method according to the present invention. In another embodiment, the processing means 23 may be part of a diagnostic device for a more general internal combustion engine or part of a personal computer (PC) .

[0046] Preferably, the processing means 23 are functionally connected with the measuring means, in particular with the multi-gas analyzer 21 by the measurement tube 22 and the pressure sensor/transmitter and the Pitot tube .

[0047] Therefore, the processing means 23 are able to combining values (expressed in ppmV or percentage) obtained from the multi-gas analyzer 21 with those (expressed in Nm³/s) obtained from the Pitot tube. This permits to have real time correlation between the exhaust gas concentration values and the overall exhaust gas output measurements and a real-time calculation/quantifying of the (real absolute) emission value (in g/km or g/km) of the corresponding exhaust gas emitted from the Diesel engine.

[0048] The processing means 23 are also functionally connected with the means for determining the at least one operating parameter, and with the analysing means. [0049] Preferably, the processing means 23 takes into account a time delay between the measure of the exhaust composition and the acquisition of operating parameters to take into account the exhaust gas transportation in the exhaust gas circuit .

[0050] Preferably, the processing means 23 are connected to the ECU 11 of the engine for acquiring the operating parameters available in the ECU and combining values of the operating conditions with the exhaust gas measurements and the overall exhaust gas output measurements allowing a real time correlation between the operating conditions and the gas measurements.

[0051] The correlation between the gas measurements, the operating parameters and/or the overall exhaust gas output measurement permits to refine the diagnostic of the Diesel engine .

[0052] For example, the measurements of the engine speed permit to improve the time measurement precision, and to automate the starting point of said measurement. The differential pressure on the filters also refines the measurements by allowing for example to determine if the exhaust line is clogged at the catalyst or at the particle filter .

[0053] The overall exhaust gas output measurements allow to define more precisely the malfunctions diagnosed using the exhaust gas measurements and the operating parameters measurements, for example regarding the leaking EGR valve, the clogging of the exhaust line or filling problems.

[0054] Furthermore, the correlation between the gas measurements, the operating parameters, and the exhaust gas output measurement, permits also a calculation of the exhaust gases (CO, C0₂, HC, NO_x) or total exhaust gas emission value (in g/h) which takes into account the temperature (in Kelvin) of the overall and/or individual exhaust gases. [0055] The diagnostic device 20 may further be protected by a filtration system.

[0056] In a preferred embodiment, the diagnostic device 20 further comprises means for calculating the individual output (or flow) value (in Nm³/s) of the at least one exhaust gas as above-described and processing means capable of calculating, based on the measure of the (concentration) level of the at least one exhaust gas and the measure of the total output (value) of the overall exhaust gases, the emission value of the at least one exhaust gas emitted by the engine and capable to compare the calculated emission value of said at least one exhaust gas with the predetermined emission limit of said at least one exhaust gas. The diagnostic device 20 may therefore also be a device for verifying compliance of the Diesel engine with the predetermined emission limit of at least one exhaust gas.

[0057] The diagnostic device 20 may further comprise printing means to print a report, or reports, related to the diagnostic of the Diesel engine, preferably to print maintenance sheets indicating the checks and repairs to be performed .

[0058] Preferably, the diagnostic device 20 according to the present invention may be incorporated in a vehicle in order to perform measurements of the engine while running or being an independent apparatus, not being part of the vehicle, an external diagnostic device which may be used in vehicle control centres or vehicle repair places.

[0059] The method according to the invention is implemented in the diagnostic device 20 using at least one software, or algorithm (modeled defaults), comprised in the processing means 23, preferably into the microcomputer, to interpret the measures performed.

[0060] The diagnostic method according to the invention will now be described in more detail with the help of table 1. [0061] The diagnostic method according to the invention allows scanning the entire working range of the engine's operation by checking all steps of combustion with their related chemical transformation. It allows in particular to very precisely diagnosing the malfunctions of the engine which are the causes of the malfunction of this engine's pollution control system.

[0062] The diagnostic method according to the present invention, is preferably implementing into a device incorporated in a vehicle in order to perform measurements of the engine while running or a device being an independent apparatus, not being part of the vehicle, an external diagnostic device used in a vehicle control centre or vehicle repair places .

[0063] Before starting the measures and the diagnostic method, the user preferably enters into the diagnostic device 20 the type of Diesel engine on which the diagnostic is to be performed (injection mode, turbocharger present or not...) .

[0064] The exhaust gas, operating parameters and overall exhaust gas emission measurements are preferably done every 500 ms . Preferably, the gas measurements are synchronised with the operating parameters acquired from the ECU. The diagnostic method according to the invention is therefore a dynamic diagnostic method.

[0065] The gas levels are expressed either in percentages or in ppm (mg/1) .

[0066] An example of the implementation of the diagnostic method according to the invention is given in table 1.

[0067] The diagnostic method comprise the step of providing a Diesel engine comprising a motor block 1, air intake means, exhaust gas outlet means and fuel injection means . Preferably providing an engine comprising an exhaust gas recirculation valve, a common rail injector system, a flow regulator of the common rail injection system, a high pressure pump, a distributor-type pump of the fuel injection system, an injection circuit, injectors, a turbocharger comprising bearings, an intake circuit, an exhaust line, and an air filling system.

[0068] Preferably, the diagnostic method is implemented on a hot Diesel engine. Preferably, the temperature of the engine is acquired from the ECU interface 30 before the beginning of the diagnostic method, the method starting only when a predetermined temperature is reached.

[0069] The diagnostic method further comprise the step of measuring, according to a predetermined state of the engine, the level, or the evolution of said level, of a first exhaust gas emitted by the internal combustion engine, said exhaust gas being selected from the group consisting in carbon dioxide (C0₂), carbon monoxide (CO), nitrogen oxides (NO_x) and unburnt hydrocarbons (HC) or a combination thereof.

[0070] The diagnostic method further comprise the step of measuring the overall exhaust gas output. This measurement is particularly important to define or refine the malfunctions of the EGR valve, the filling problems, and the exhaust line clogging.

[0071] The diagnostic method further comprise the step of measuring at least one operating parameter being selected from the group consisting of engine speed, engine charge, i.e. the accelerator pedal position, air inflow, forced induction pressure, water temperature, exhaust gas temperature, pressure of the high pressure feeding circuit, fuel inflow, set point of opening of the exhaust gas recirculation valve, individual injector volume correction, exhaust gas temperature, differential pressure on the particulate filter or a combination thereof.

[0072] The operating parameters are preferably those available from the ECU 11, which are acquired continuously during all phases of the diagnostic. More particularly, at least the engine speed is recorded throughout the test, to verify that the target operating conditions are reached, and eventually in order to synchronise the different measurements .

[0073] The diagnostic method further comprise the step of analysing and deducing from the measures performed a malfunction affecting the engine.

[0074] For example, during the first idle, the level of unburnt hydrocarbons (HC) is measured and the engine speed confirms that the idle is reached. A hydrocarbon (HC) level higher than 100 ppm at idle is the sign of a significant problem with the injection circuit corresponding to a seizing of the injectors. In this case, the diagnostic method will not be able to continue and the diagnostic device will display this anomaly. It will then be necessary to check the injectors and the diesel oil circuit. This measure allows also to test whether the collection tube 22 was actually introduced into the exhaust line .

[0075] After the first idle, the engine is shut down. The duration of this phase is variable depending on the level of carbon dioxide (C0₂) . Initially planned to last 50 seconds, it may extend itself 60 seconds longer if the value of this exhaust gas is too high to detect and analyze the increase of the carbon dioxide (C0₂) during the starting of the engine in the following step.

[0076] A overall exhaust gas emission value different from zero allows to determine that the exhaust line did not evacuate all the exhaust gases and still release some. Furthermore, a differential pressure on the particulate filter different from zero permits to determine that the particulate filter is involved.

[0077] The engine is then started and the idle is maintained. During this phase, the proper operation of the EGR valve and of the pump and injectors is analyzed.

[0078] Several checks are carried out: the operation of the control of the EGR valve (command in closed position), the operation of the EGR valve through the carbon dioxide (C0₂) value, the level of which must increase with its opening, the operation of the EGR valve through the nitrogen oxide (NOx) value, the level of which must drop consecutively to its opening and the level of gas recirculated through the carbon dioxide (C0₂) value.

[0079] The EGR valve opening implies a diminution of the air inflow and an EGR percentage different of zero, the total exhaust gas emission decreasing as the EGR opens.

[0080] The increase in pressure of the diesel oil circuit is checked through the increase time of the carbon dioxide (C0₂) value (increased pressure of the pump) and through the pressure which increases up to a value comprised between 240 to 300 bars.

[0081] The spraying of the injectors is checked through the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) values and through the temperature of the particulate filter which may be higher then 160 °C.

[0082] The injection point is checked through the carbon monoxide (CO) and nitrogen oxide (NOx) values and through the water temperature .

[0083] The compression of the engine (general condition of the mechanics) is check through the hydrocarbon (HC) and carbon monoxide (CO) values, the air filling coefficient of the engine through the combination of the carbon dioxide (C0₂) and oxygen (0₂) values and through the air inflow and the total exhaust gas emission which may be low.

[0084] The carbon dioxide (CO2) level, after starting up of the engine, must quickly reach 1.7% to 2.7%, which means that the quantity of diesel oil injected is correct. Then it must increase proportionally to the opening of the EGR valve without exceeding a value of 5.6%. The pressure of the high pressure feeding circuit must quickly reach 240 bars and the fuel inflow a minimum of 5 mm³/stroke.

[0085] The engine runs then at 1200 rpm. At this speed, there is a balance between the manifold pressure and the atmospheric pressure. This enables the detection of any air scoop on the intake circuit. The levels of nitrogen oxide (NOx) and carbon monoxide (CO) allow highlighting this malfunction. The nitrogen oxide (NOx) value must drop significantly and the carbon monoxide (CO) value remains the same, relative to the idle speed.

[0086] The engine runs then at a speed between 3000 and 3500 rpm. Over this range of speed, the EGR valve must be closed. During this phase, the following points are checked :

- closing of the EGR valve through the decrease of the carbon dioxide (C0₂) value. For an EGR position of zero percent, the carbon dioxide value should decrease and the overall exhaust gas output should increase;

- sealing of the EGR valve through the carbon dioxide (C0₂) level. For an EGR position of zero, the carbon dioxide value should reach a predetermined value determined for a normal state of the engine;

- sealing of the main turbocharger bearings through the hydrocarbon (HC) value;

- the closed EGR valve filling coefficient through the combination of the carbon dioxide (C0₂) and oxygen (0₂) levels and through a air inflow, through a forced induction pressure and an overall exhaust gas output low;

- the injection timing through the carbon monoxide (CO) and nitrogen oxide (NO_x) values and through the water temperature .

[0087] The Engine runs then at full load. This test is done with accelerator wide open at the maximum governing speed. During this phase, the following points are checked: internal leaks of the injectors through the carbon dioxide (C0₂) value, and through the pressure of the high pressure feeding circuit which will not be correct and which could decrease between the beginning and the end of the full load step; - the flow regulator on common rail systems through the carbon dioxide (C0₂) level, and through the accelerator pedal position which should be at 100%, and the pressure of the high pressure feeding circuit which may not be stable and may increase;

- operation of the turbocharger through the carbon dioxide (C0₂) value, and through a low forced induction pressure and air inflow;

insufficient filling of the engine with oxygen, for example due to clogging of the intake manifold, by taking the combination of oxygen (0₂) and carbon dioxide (C0₂) into account, and trough an insufficient air inflow (lower then 700 mg/stroke), a low forced induction pressure and low air inflow;

- the flow of the high-pressure pump through the carbon dioxide (C0₂) value, through a low quantity of diesel injected and low pressure of the high pressure feeding circuit ;

- the spraying of the injectors through the nitrogen oxide (NO_x) level and through a exhaust gas temperature being higher then 400°C.

[0088] The engine returns to idle. This phase allows confirming the proper or improper operation of the EGR valve as well as its control. It is also possible to check the sealing of the main bearings of the turbocharger.

[0089] During this phase, the EGR valve should be open and the opening percentage should be different from zero. The air inflow should be comprised between 170 and 270 mg/stroke. A differential pressure on the particulate filter lower then 100 mbars would suggest that the particulate filter is partially clogged.

[0090] The engine is then shut down. During this phase, any clogging of the exhaust line will be highlighted through the carbon dioxide (C0₂) and oxygen (0₂) values (the 0₂ level must quickly reach 20% and the carbon dioxide

(C0₂) level must tend toward zero) . In the event of clogging of the exhaust line, the exhaust gas recirculation level will be too high and will lead to a malfunction of the pollution control circuit. The differential pressure on the particulate filter and the overall exhaust gas output should quickly reach zero.

TABLE 1

[0091] The different engine phase of the test protocol to implement the method according to the invention are performed by a person which operates the vehicle under the instructions provided by the diagnostic device 20.

[0092] The various malfunctions of the Diesel engine which may be detected and characterized using the diagnostic device 20 and the diagnostic method according to the invention will be described now in more detail.

[0093] 1. EGR valve not controlled or neutralized.

As indicated above, the EGR valve enables the recirculation of part of the exhaust gases in the intake so as to limit the presence of nitrogen oxides (NO_x) . To check whether the EGR valve is controlled or neutralized, the carbon dioxide (C0₂) value is analyzed and must increase when the EGR valve is opened. The carbon dioxide (C0₂) value, EGR valve closed, at idle, is normally between 1.6% and 2.7%. Assuming that 100% of these carbon dioxide levels are recycled, then the carbon dioxide (C0₂) level should be within a range between 3.2% and 5.4%. If these values are between 1.6% and 2.7%, on both idle phases of the diagnostic method, this means that the EGR valve is not commanded by the computer, for example due to a defective air flowmeter, or neutralized (blocked in the closed position) .

[0094] The acquisition by the means measuring the operating parameters of the set point of the EGR permits to make the difference between the absence of command and blocking of the EGR valve. The absence of command is identified by an air inflow of around 450 mg/stroke and an opening of the exhaust gas recirculation valve of zero percent. The EGR valve blocking is indentified by an air inflow of around 450 mg/stroke and an opening of the exhaust gas recirculation valve being different of zero percent .

[0095] 2. Defective or non-sealing EGR valve.

The EGR valve is commanded according to speed ranges taken into account by the protocol: toward 3000 rpm, in practice between 2700 rpm and 3000 rpm, the EGR valve is in closed position and therefore there is a recirculation of exhaust gases in the intake, which normally creates a drop of the carbon dioxide level with no decrease of the overall exhaust gas output. If the EGR valve is defective the opening of the exhaust gas recirculation valve would not be consistent with the engine speed, for example an EGR opening different from zero and an engine speed at idle an air inflow lower then 180 mg/stroke .

[0096] Moreover, if the EGR valve lacks sealing due to fouling, the carbon dioxide (C0₂) value will be equal to, or higher than, the levels measured during the idle and 1200 rpm phases (at idle, during opening of the EGR valve, the recirculated carbon dioxide (C0₂) value is higher then 2.7% and must not exceed the value of 5.8% and even, preferably, 5.6%), the air inflow being lower then 450 mg/stroke. At 3000 rpm, with an opening of the EGR valve being at zero percent, the air inflow and the overall exhaust gas output will be low. In this respect, significant clogging of the exhaust line may be at the origin of the fouling of the EGR valve.

[0097] 3. Clogged exhaust line.

The role of the exhaust line is crucial as it takes part in the reduction of decibels of the engine and the evacuation of burned gases. On vehicles with pollution control system, the exhaust line is equipped with an oxidation pipe (catalyser) or an oxidation pipe and a particle filter. These elements must have a minimum of load loss to operate well. Any engine unit problem, driving a discharge of unburnt gases and soot and particles in too large a quantity, will clog the exhaust line. Moreover, this will cause an excess of re-circulated exhaust gas in the intake through the EGR valve, thereby increasing the initial malfunction and causing a higher quantity of polluting gases to be discharged. This has significant consequences for the operation of the engine. In extreme cases, it may prevent the engine from starting up. It is during the last phase of the protocol, engine cut, that the exhaust line is checked. When the engine is shut down, the carbon dioxide (C0₂) value must quickly fall to a value below 1% and the oxygen 0₂ value must, likewise, exceed 20%. If these levels are not reached at the end of 40 seconds, or if the differential pressure on the particulate filter is different from zero, the exhaust line is considered to be clogged.

[0098] 4. Filling problem.

Filling is the physical capacity of the engine to admit air.

In a Diesel engine, air compression enables the ignition of the diesel oil through the elevation of the temperature in the cylinder. A deficient quantity of air admitted into the engine causes the following malfunctions:

too long an ignition delay with, as consequences, a formation of soot and particles,

- an increase in consumption with loss of power observed on the road,

- smoke at the exhaust during acceleration.

[0099] The possible causes of a filling problem are a clogging of the exhaust line, a clogging of the intake conduit, a non-sealing EGR valve, a defective turbocharger solenoid valve, a defective turbocharger, incorrect clearance at the valves or a wearing of the engine.

[0100] As the atmosphere is made up of approximately 20.9% oxygen (0₂) per air contents, and taking the combustion of the hydrocarbons (HC) into account upon combustion in the idle phase, the addition of oxygen (0₂) and carbon dioxide (C0₂) levels must be at least equal to 19% during the fully loaded phase. Otherwise, the engine has insufficient filling.

[0101] The measurement, by the means measuring the operating parameters, of the operating parameters, overall exhaust gas output measurement and air intake, permits to refine this diagnostic by indicating which part of the engine

(injectors, exhaust line...) is affected.

[0102] 5. Internal leak of the common rail injectors.

The common rail injectors of the engine are of the electrohydraulic type. On the hydraulic level, they are equipped with two chambers (upper and lower) in which the balance or imbalance of pressure allow to maintain the needle of the injector either in the closed position, or in the open position. An internal circuit allows connecting these two chambers and ensuring the return of diesel oil. When there is an internal leak on the injector return, the quantity of fuel (pressure decrease) and the moment of passage into the open position of the needle of the injector are modified. This causes a lack of performance (correction of the injection point and lack of flow) . In the case of a significant loss, this malfunction may even prevent the engine from starting. Revealing internal leaks on the injectors is done at 1200 and 3000 rpm through an increase in carbon monoxide (CO) relative to the idle phase, or fully loaded, by a carbon dioxide (C0₂) level dropped by 1 to 5% between the beginning and the end of the phase. The two analyses may, of course, be done to complement one another .

[0103] The measurement of the injectors volume correction permits to identify which injector is involved in the malfunction.

[0104] 6. Checking the flow regulator of the high-pressure (HP) pumps on the common rail system.

The common rail system is equipped with a HP pump, which generates pressure according to the load and speed. The quantity of diesel oil injected into the combustion chamber, per cycle, depends on this pressure. The flow regulator serves to inject the necessary and sufficient quantity of diesel oil, which results in greatly limiting the temperature of the fuel at the level of the return circuit in the tank. When the flow regulator is defective, the optimal quantity of diesel oil will not be injected into the cylinders, which will result in decreasing the engine's performance. Identify the malfunction of a flow regulator is done at full load, when the pump provides maximal pressure on its first two pistons. When the flow regulator is hydraulically defective, the maximal pressure (700 bars) is not immediately reached, and the fuel inflow is not constant, the normal value being comprised between 7 to 9 mg/stroke for EURO 4 engines and around 5 mg/stroke for EURO 5 engines. This will be translated in carbon dioxide (C0₂) level, connected to the quantity of diesel oil injected and burned, showing an increase in its values between the beginning and the end of the full load phase. This increase of volume concentration (C0₂) must be higher than 8% to validate the malfunction.

[0105] 7. Defective high pressure pump.

The high pressure pump allows to generate a diesel oil pressure depending on the engine speed and the load (in practice up to 1300 bars; 1 bar = 10⁵ Pa) . This pressure is variable according to the types of pump and the systems used. One visualizes the increase in pressure of the pump through the carbon dioxide (C0₂) slope upon start-up of the engine, but also at its maximal value at idle (EGR valve closed) . The carbon dioxide (C0₂) increase phase until stabilized idle must not exceed 4 seconds and its value must exceed 1.6%, and even 1.7% in practice. During the fully loaded phase, the pump must deliver at full flow on its first two pistons. If this is defective, the carbon dioxide (C0₂) value will not exceed 2.5%. On a distributor-type fuel injection pump, although its operating principle is different, the values will be identical .

[0106] The measurement, by the means measuring the operating parameters, of the fuel inflow and pressure on the common rail can refine the diagnostic and allows determining if there is a sealing problem on the high pressure feeding circuit or a bad fuel injection control, for example when the pressure of the high pressure feeding circuit is good while the fuel inflow is high.

[0107] 8. Poor spraying of the injectors.

The quality of the spraying of the injectors is essential to ensure optimal combustion of all the diesel oil injected into the combustion chamber. Otherwise, the post combustion will extend and generate an increase in the temperature with significant formation of nitrogen oxides (NO_x) . There will also be unburned elements in the form of residual hydrocarbons (HC) and carbon monoxide (CO) ( (HC) level higher than 10 ppm and CO value higher than 0.05%, regardless of the speed) . During improper spraying of the injectors, the level of nitrogen oxides (ΝΟχ) will depend on the type of injection. For direct injection, a level higher than 120 ppm at idle (EGR valve open) and value higher than 300 ppm fully loaded, and for indirect injection, level higher than 120 pm at idle (EGR valve open) and value higher than 250 ppm fully loaded, is a sign of a malfunction.

[0108] In this case, the measurement of exhaust gas temperature and/or injectors volume correction can improve the diagnostic. At idle, the temperature should not exceed 160 °C and 400°C at full load. The injectors volume correction indicates the injector which is defective.

[0109] 9. Leaks on turbocharger main bearings .

The turbocharger allows increasing the air filling of the engine, and therefore its performance. It is a rotating device which uses the pressure from the exhaust gases to suck up and compress the outside air admitted into the engine. The blade and the axis of the turbocharger can exceed a speed of rotation of 150,000 rpm. At this speed, any lubrication flaws will cause the destruction of the bearings and the turbocharger. Breaking of the bearings causes the oil to be sucked up again and the engine to race until it breaks. An oil leak on a turbocharger bearing is a worrisome sign of wear. A leak on the turbocharger bearings may be diagnose at the speed of 3000 rpm, by a level of hydrocarbons HC increasing in relation to the values measured at idle and at 1200 rpm, and similarly during the fully loaded phase, a level of hydrocarbons HC higher than the values measured at 3000 rpm, and upon return to idle, a level of hydrocarbons HC exceeding the value of 40 ppm.

[0110] 10. Defective turbocharger. When the turbocharger is defective, due to a seized blade or a cutting of the supercharging pressure in particular, the filling coefficient will drop significantly. At full load, the addition of the oxygen (0₂) and carbon dioxide (C0₂) levels will then be less than 19% with a carbon dioxide (C0₂) value higher than 8% and an oxygen (0₂) level less than 10.5%.

[0111] In this case, the measurement of the air flow and the forced induction pressure improves the diagnostic. An air flow lower then 600 mg/stroke and a forced induction pressure lower then 2000 mbars permits to confirm the turbocharger malfunction. Furthermore, an overall exhaust gas output will be to lower regarding the engine speed.

[0112] 11. Injection advance excess

A diesel oil injection done too early causes too quick an increase in pressure in the cylinder, characterized by engine rattles. On vehicles equipped with a distributor-type fuel injection pump, blocking is necessary, but on common rail systems, it is necessary to act on the origin of the malfunction because there is no manual blocking action. An advance excess is characterized, for a direct injection, by, at idle, EGR valve open, a carbon monoxide (CO) level below 0.005% with nitrogen oxide (NO_x) value higher than 140 ppm, and for an indirect injection, at idle, EGR valve open, a carbon monoxide (CO) value below 0.005% with nitrogen oxide (NO_x) value higher than 90 ppm.

[0113] In this case, the measurement, by the means measuring the operating parameters, of the water temperature, which should be stable and not be lower than 80°C, indicates a sensor malfunction.

[0114] 12. Lack of injection advance.

A lack of advance is characterized by a performance deficiency due to combustion still present during the descent of the piston. The diesel oil injected therefore cannot burn correctly because when the piston descends, the temperature drops. During a lack of advance, the remarkable values of the gas will be for a direct injection: . at idle, a carbon monoxide (CO) level higher than 0.02% with nitrogen oxide (NO_x) value less than 90 ppm;

. at a speed of approximately 3000 rpm, a carbon monoxide (CO) level higher than 0.02% with nitrogen oxide (NOx) value higher than 100 ppm.

And for indirect injection:

. at idle, a carbon monoxide (CO) level higher than 0.02% with nitrogen oxide (NO_x) value less than 60 ppm.

. at a speed of approximately 3000 rpm, a carbon monoxide (CO) level higher than 0.02% with nitrogen oxide (NO_x) value higher than 60 ppm.

[0115] 13. Air scoop on the intake circuit.

When the engine turns at approximately 1200 rpm, there is balancing of the manifold pressure with the atmospheric pressure. This allows detecting any air scoop on the intake circuit. To highlight this malfunction, the levels of nitrogen oxides (NO_x) and carbon monoxide (CO) are taken into account. In practice, the nitrogen oxide (NO_x) value should drop significantly and the carbon monoxide (CO) value should remain identical, in relation to the idle speed. Furthermore, the air inflow should be lower than 230 mg/stroke in idle for EURO 4 engines and lower than 170 mg/stroke at idle for EURO 5 engines .

[0116] 14. Flow problem.

As indicated previously, the diesel oil flow is controlled by the values of C0₂ over the entire range of speeds. A problem on the diesel oil flow is indicated by a C0₂ value of less than

1.7% at idle, which not exceed 2.5% at full load. Furthermore, the pressure of the high pressure feeding circuit at idle should be comprised between 240 and 300 bars and the fuel inflow should be stable, between 7 to 9 mg/stroke for EURO 4 engines and around 5 mg/stroke for EURO 5 engines.

[0117] The diagnostic method according to the present invention implements a dynamic monitoring of the combustion of the Diesel engine, in particular through the measurement of the level of at least one of exhaust gas, or a combination of two different gases, for a predetermined engine speed, and the level of a same gas at two different moments of a stabilized engine speed, or over two different ranges of engine speeds, or for two different states of an engine element, in order to determine a state resulting from the sum of the volume concentrations of two different gases, or of a variation of concentration of a same gas, in order to establish, in combination with operating parameters and/or overall exhaust gas output measurements, the existence of a given malfunction in case of drift relative to a reference state.

[0118] For each diagnostic phase of the diagnostic method according to the invention and each engine malfunctions described above, the measurement of the at least one operating parameter and/or of the overall exhaust gas output allow the diagnostic method and diagnostic device to be more precise and more accurate. Indeed, by tacking into account the at least one operating parameter during the measurement of the at least one exhaust gas ensure that the predetermined state of the engine which should be reached for the measurement is actually reached and correctly reached. Furthermore, it allows a real time correlation between the operating conditions, or predetermined state of the engine, and the gas measurements. Therefore, the analysis of level, or the evolution of said level, of the exhaust gas, i.e. comparison between the measures obtained during the diagnostic and the ones known to be characteristic of one or several predetermined normal or abnormal states of the engine, is more precise. Therefore, the malfunctions affecting the Diesel engine are more accurately and reliably determined.

[0119] Furthermore, the diagnostic method may also permit to verify the compliance of the Diesel engine with the pre-determined emission limit of at least one exhaust gas.

[0120] The diagnostic method may therefore further comprise the step of calculating, from the measuring of the level (in ppmV or percentage) of the first exhaust gas and of the overall exhaust gas output (or flow) value (in Nm³/s), the emission value (in g/km or g/h) of the at least one exhaust gas emitted by the internal combustion engine, and comparing the calculated emission value of the at least one exhaust gas with a pre-determined emission limit of said at least one exhaust gas .

[0121] The measurement of the output of the at least one exhaust gas is performed by measuring of differential pressure, preferably by using a Pitot tube.

[0122] The calculation of the exhaust gas emission value (in g/km or g/h) may also takes into account at least one operating parameter, in particular the temperature (in Kelvin) of the overall (and/or individual) exhaust gases, fuel inflow or fuel consumption (in 1/km or mm³/stroke) which may be provided by the ECU 11.

[0123] Calculating the exhaust gas emission value and expressing it (in g/km or g/h) is of particular interest as this corresponds to the officially recognized unit for indirectly quantifying the polluting character of an engine . Also, this particular unit is the one which is taken into account by governments when awarding bonuses to purchasers of "clean" motorized cars .

[0124] Accordingly, the method and device according to the present invention allow real-time and on-demand checking of compliance of an internal combustion engine with pre- established exhaust emission limits. In particular, the method and apparatus of the invention permits verifying, at any time during the lifetime of an engine, whether it still complies with a pre-established exhaust emission limit that it did comply with at a certain period in the past, in particular when the engine was brand new, and permits detecting the engine malfunctions involved in the non-compliance with exhaust emission limits of the engine.

[0125] Of course, the present invention is not limited to the embodiments described and illustrated herewith.

Claims

1. A diagnostic method for a Diesel engine for determining whether said engine is affected by one or several malfunctions negatively impacting the degree of pollution of the exhaust gases produced by said engine, comprising the steps of:

a) providing a Diesel engine comprising a motor block 1, air intake means, exhaust gas outlet means and fuel injection means .

c) measuring the overall exhaust gas output,

e) analysing the measures performed at steps b) and d) or at steps b) , c) and d) by a comparison of said measures with the ones being characteristic of one or several predetermined normal or abnormal states of said engine,

f) deducing from the analysis of said measures, a malfunction affecting said engine.

2. The method according to claim 1 wherein steps b) and d) or b) , c) and d) are performed simultaneously.

3. The method according to any of the preceding claims, wherein the level or evolution of the level of the first exhaust gas is measured in combination with the level, or evolution of the level, of at least another exhaust gas, said another exhaust gas being oxygen when the first exhaust gas is carbon dioxide, or said another exhaust gas being unburnt hydrocarbons or nitrogen oxides when the first exhaust gas is carbon monoxide.

4. The method according to any one of the preceding claims, wherein, according to a predetermined operating state of the engine, the level of the first exhaust gas, alone or in combination with at least another exhaust gas, is measured and compared to a first level of said exhaust gas measured for a state representing a normal operation of said engine and/or compared to a second level of said exhaust gas measured for a state representing a abnormal operation of said engine and characterizing a predetermined malfunction, and from said comparison, deducing that said engine is affected by said predetermined malfunction.

5. The method according to any of the preceding claims, wherein the step c) is performed by measuring of differential pressure.

6. The method according to any of the preceding claims, wherein the step c) is performed with a Pitot tube.

7. The method according to according to any one of the preceding claims, further comprising the steps of:

- calculating, from the measuring of steps b) and c), the emission value (in g/h or g/km) of the at least one exhaust gas emitted by the internal combustion engine, and

- comparing the calculated emission value of the at least one exhaust gas emitted by the internal combustion engine with a pre-determined emission limit of the at least one exhaust gas.

8. A device to diagnose a Diesel engine malfunction negatively impacting the degree of pollution of the exhaust gases produced by said engine, said device comprising :

- means for measuring at least a first exhaust gas selected from the group consisting in carbon dioxide (C0₂), carbon monoxide (CO), and unburnt hydrocarbons (HC) and nitrogen oxides (NO_x) , or a combination thereof,

- means for measuring the total output of the overall exhaust gas, and

means for measuring at least one operating parameter selected from the group consisting of engine speed, engine charge, air inflow, forced induction pressure, water temperature, pressure of the high pressure feeding circuit, fuel inflow, set point of opening of the exhaust gas recirculation valve, individual injector volume correction, exhaust gas temperature and differential pressure on the particulate filter,

- means for analysing the level, or evolution of the level, of said exhaust gas and said overall exhaust gas output, and analysing said operating parameters, or the evolution of said operating parameters, performing a comparison with the ones being characteristic of one or several predetermined normal or abnormal states of said engine,

- processing means 23 enable to characterize a malfunction affecting said engine.

9. The device according to claim 8, wherein the means for measuring at least a first exhaust gas comprise at least one gas analyzer 21 comprising at least one measuring cell.

10. The device according to claim 8 or 9, further comprising means for calculating the emission value of the at least one exhaust gas with a pre-determined emission limit of said at least one exhaust gas .

11. The device according to any of the claims 8 to 10, wherein the means for measuring the total output of the overall exhaust gas operate by measuring of differential pres sure .

12. The device to any of the claims 8 to 11, wherein the means for measuring the total output of the overall exhaust gas comprise a Pitot tube.

13. Computer program executable on the device according to any of the claims 8 to 12 containing instructions that, when executed, perform the method steps of the method of any one of the claims 1 to 7.